This invention relates generally to improvements in impact type hand tools such as hammers and mallets and the like, and to related processes for manufacturing such hand tools. More particularly, this invention relates to an improved hammer of the type having a tool head of hardened steel or the like, such as a carpenter's framing hammer, wherein the tool head contains a movable filler material to provide the hammer with nonrecoil or deadblow characteristics during normal use.
Hammers of the type have a tool head defining one or more metal impact members are well known in the art, for use in striking a target or work surface. In this regard, such hammers are available in a broad range of tool head sizes, shapes and weights in accordance with the particular task or tasks to be performed, such as driving nails or breaking concrete. Since marking or other damage to the target surface is frequently not an issue, the tool head is commonly constructed from a tough grade and preferably hardened steel to provide durable impact members for extended service life. One example of such hammers comprises a conventional carpenter's framing hammer having a hardened steel tool head with a central aperture or eyehole for assembly with a tool handle, wherein the tool head defines an impact member and a nail removal claw at opposite ends thereof. The tool head of such framing hammer is used for a variety of tasks, including driving nails, removal of nails, and other prying and wedging functions.
One problem encountered with traditional hammers of the type having a metal tool head relates to hammer rebound or recoil from a target surface after striking an impact blow. More specifically, when the hammer is swung by a worker to strike a target surface, most of the kinetic energy is transmitted from the impact member of the hammer to the target surface at the moment of impact. However, a portion of this kinetic energy is not transmitted to the target surface, but instead causes the hard-faced tool head to rebound or recoil from the target surface. This rebound effect thus prevents complete or substantially complete energy transfer to the target surface, thereby typically requiring an increased number of impact blows to perform a given task, e.g., driving a nail. Alternately, this rebound effect requires the worker to swing the hammer with an increased force, or to use a hammer with a heavier tool head, in order to complete a task with a reduced number of impact blows. Moreover, the worker must maintain a grasp of the hammer following an impact blow with sufficient strength to resist rebound forces in order to prevent loss of control. All of these factors undesirably increase the degree of strength and skill required for proper and safe hammer usage.
Nonrecoil or so-called deadblow hammers have been developed in an attempt to reduce or eliminate rebound of the tool head from a target surface following an impact blow. Such nonrecoil or deadblow hammers typically have a tool head defined by a hollow core canister filled partially with a relatively high mass and flowable filler material such as steel shot pellets, steel pins, or the like. In many designs, the hollow canister is protectively encased in whole or in part within a molded jacket or cladding constructed from a selected tough and durable thermoplastic material such as nylon. In use, when the tool head is impacted with a target surface, the filler material shifts and slides about within the hollow canister to absorb and dissipate the impact force in a manner which effectively counteracts any resultant rebound force. As a result, a greater proportion of the kinetic energy is transmitted from the tool head to the target surface in the course of each blow, to permit performance of a given task in a reduced number of blows, or alternately to permit use of a hammer having a lighter tool head. In addition, less strength and skill are required to control the hammer following each blow. For examples, of such nonrecoil impact tools, see U.S. Pat. Nos. 5,262,113 and 5,375,486. However, nonrecoil hammers have generally been limited to mallets and the like having relatively soft impact faces designed to avoid marking or damage to the target surface, or alternately to include metal-faced caps designed to mount upon a tool head formed primarily from relatively soft or nonmetallic materials. Such hammers have generally been ill-suited for use, for example, in a typical carpentry or framing environment wherein a hardened steel tool head is desired.
The present invention relates to an improved hammer or other striking tool of the type having a rigid tool head of hardened steel or the like to define at least one hard-faced impact member, wherein the tool head contains a flowable or movable filler material of relatively high mass to provide the hammer with substantial nonrecoil characteristics following an impact blow to a target surface.